A fuel cell system which circulates fuel gas includes a gas-liquid separator in a fuel gas circuit because the fuel gas discharged from a fuel electrode is mixed with generated water. The gas-liquid separator separates the liquid water from the gas component so that only the gas component is fed to the fuel electrode again. In the process of discharging the water separated from the fuel gas to the outside of the system, the separated water is temporarily stored in a tank. Thus, water constantly exists in a discharge section and blocks the fuel gas channel from the outside, thereby preventing the flammable fuel gas from being discharged to the outside in the drainage process.
If, for example, a fuel cell vehicle is parked in sub-zero temperatures and water in the tank freezes, it becomes necessary to melt the ice in the tank. The water cannot be discharged until the ice is melted. Therefore, in the case where the time required for melting the ice is long, there is a possibility that the generated water will overflow from the tank if, for example, the output of the fuel cell is set to a high level immediately after the activation thereof. In such a case, gas-liquid separation cannot be performed and fuel gas necessary for power generation cannot be supplied to the fuel electrode. As a result, power generation cannot be performed. Therefore, a warm up operation of the fuel cell is performed until the ice is completely melted and the vehicle cannot be started until after the ice is completely melted.
A method for reducing the time required for melting the ice in the tank to allow the vehicle to be started in a shorter time is proposed in the related art. Heat sources are placed on the exterior of and interior of the tank, and the ice in the tank can be heated from both the inside and outside.
The above-described method of the related art has the following disadvantage. That is, there may be a case where the ice at positions where the heaters are placed can be rapidly melted, whereas the time required for melting the ice at positions other than the positions where the heaters are placed is still long. If the vehicle is started in such a state, the water level largely varies in accordance with the amount of water that flows into and out of the tank. Therefore, it is still difficult to control the water drainage from the tank and it is difficult to start the vehicle in a short time.
An object of the invention to overcome the above-describe disadvantage of the related art.